Complex compounds which contain, as their central atoms, metals of Group VIII A of the Periodic Table (IUPAC version), P(III) compounds such as phosphines as ligands, and optionally further groups capable of complex formation, have in recent years gained increasing importance as catalysts. Thus, the reaction of olefins with synthesis gas to give aldehydes (hydroformylation), which is practiced on a large scale in industry, is carried out in the presence of catalysts which comprise cobalt and particularly rhodium and triphenylphosphine. In accordance with the solubility of these catalysts in organic media the reaction proceeds in a homogeneous phase.
This reaction, like other stoichiometric and catalytic reactions, can also be carried out in heterogeneous reaction systems. This original development is not limited to complex compounds of metals of group VIII A, but also includes complex compounds of groups VII A and I B of the Periodic Table (IUPAC version) as catalysts. The use of catalysts dissolved in water permits them to be separated from the water-insoluble reaction product simply and gently.
For example, the process described in DE-C-27 00 904 for the addition of hydrogen cyanide to an unsaturated organic compound having at least one ethylenic double bond is carried out according to this principle. Suitable catalysts for this reaction are nickel/TPPTS [TPPTS is tris(m-sulfophenyl)phosphine], palladium/TPPTS or iron/TPPTS. According to DE-C-26 27 354, aldehydes are prepared by reaction of olefins with carbon monoxide and hydrogen using rhodium as metal or in the form of one of its compounds, together with a water-soluble phosphine (for example TPPTS), as the catalyst. Further catalysts of the type mentioned and their use in various reactions such as hydrogenations, allene/alkyne coupling, and amine addition to double bonds are the subject of, for example, EP-A-372 313.
Sulfonated phenylphosphines can be obtained by the process described in J. Chem. Soc., 1958, pages 281-282 by reacting triphenylphosphine with oleum, heating the reaction mixture in a water bath, diluting the reaction product with water, and neutralizing with sodium hydroxide. The sodium salt of m-sulfophenyldiphenyl-phosphine crystallizes from the sulfonation mixture.
Similar processes are also used to obtain disodium salts of di(m-sulfophenyl)phenylphosphine and tri(m-sulfophenyl)phosphine. The starting material in both cases is again triphenylphosphine which is reacted with oleum at temperatures between 18.degree. and 40.degree. C. for from 15 to 63 hours. The reaction product is diluted with water and neutralized with sodium hydroxide, care having to be taken that, during the addition of the sodium hydroxide, the temperature of the mixture is maintained below 20.degree. C. (DE-C-26 27 354). Apart from monophosphines, sulfonated di- and polyphosphines are also used as components of catalysts. Examples of the preparation thereof are given in DE-A-40 40 314.
A disadvantage of all known processes for obtaining sulfonated arylphosphines is the undesired formation of phosphorus/oxygen compounds, i.e. the oxidation of the trivalent phosphorus to the pentavalent form by the sulfur trioxide. The resulting phosphine oxides do not form catalytically active complex compounds with metal ions, and are thus worthless as catalyst components. They are therefore customarily selectively removed from the mixture of the sulfonation products, so as not to excessively burden the catalyst solution with inert materials. To limit the oxidation, the sulfonation is carried out at temperatures which are as low as possible. This measure leads to the formation of water-soluble phosphines in which the maximum possible degree of sulfonation and thus the highest solubility in water--which is important for the retention of the metal component of the catalyst system in the water--are not achieved. More extensive sulfonation by increasing the reaction time has the drawback that the oxidation simultaneously increases.